Easier way to remove particles textures from ripped model?
The black, white or grey images are most likely masks, for example a specular mask will define where the specular is high (white) and where there is no specular (black) with grey being in the middle. These 'maps' can also be used to adjust many settings like transparency, emission, mirror... instead of having one value used over the entire model.

The blue/purple images are normal maps. To get low poly objects looking detailed it is common to sculpt or model a high poly version and then bake the difference into a normal map to get a visually similar result with less geometry, these maps predominantly have a distinct blue to purple colouring.

To the issue of removing duplicate faces - if you know the material used on faces that you want to delete then you can select all the faces using that material and delete them. The technique to apply different materials to parts of a model should explain how to select faces used by a material. You could also select the faces used by the material you want to keep then invert the selection with &#9096; CtrlI and delete those faces.

As you mention many materials in use, you may also want to use python to go through them all. If you want to keep one or two materials and delete the others then a small script like this might help.

import bpy
import bmesh

me = bpy.data.objects['model2808'].data
bm = bmesh.new()
bm.from_mesh(me)

for f in bm.faces:
    if objmats[f.material_index].name != 'Material.002':
        bm.faces.remove(f)

bm.to_mesh(me)
bm.free()